The global internet has become a mass media on par with radio and television. As a mass media, it has become an invaluable tool for companies wishing to advertise and directly communicate with customers. One of the simplest features of the global Internet, electronic mail, is also one of its most powerful tools. With electronic mail (email), a user of the Internet can send a message to any other user on the internet. With the advent of HTML formatted email messages, email can now contain images and hyperlinks to other resources. Additional files, such as programs or data, can also be enclosed within email. Thus, even though email is one of the oldest internet applications, it remains one of the most important.